Integrated information theory (IIT) 4.0: Formulating the properties of phenomenal existence in physical terms
Fig 2
Composition and causal distinctions.
Identifying the irreducible causal distinctions specified by a substrate in a state requires evaluating the specific causes and effects of every system subset. The candidate substrate is constituted of two interacting units S = aB (see Fig 1) with TPMs and
as shown. In addition to the two first-order mechanisms a and B, the second-order mechanism aB specifies its own irreducible cause and effect, as indicated by φd > 0.